Many A/D converters suffer from a differential non-linearity error. This error may be caused by inaccuracy in capacitor sizing. This inaccuracy often causes missing codes in the output of the A/D converter. This results in granularity in the A/D converter and effectively reduces a dynamic range of the A/D converter output.
These missed codes often occur at the transition between most significant bits. For example, an incremental voltage beyond the voltage yielding the code 0111111 yields a code 1000011. This means that the codes between 0111111 and 1000011 are never used.